1. Field of the Invention
This invention relates to wafer level packages, and, more particularly, to a wafer level package having a pressure sensor and a fabrication method thereof.
2. Description of Related Art
A pressure sensor uses pressure sensing elements to sense gas or liquid pressure. With the rapid development of micro electromechanical systems (MEMS), a pressure sensor fabricated by micro electromechanical elements is popular in the art.
FIG. 2 shows a package having a pressure sensor according to the prior art, which generally employs an LGA package structure. The package comprises a substrate 30, micro electromechanical elements 31 disposed on the substrate 30, sensor film 32 installed on the micro electromechanical elements 31, a cavity chamber 35 formed between the sensor film 32 and micro electromechanical elements, bonding wires 33 electrically connected to the substrate 30 and the sensor film 32, a lid 34 installed on the substrate 30 that covers the micro electromechanical elements 31, and an opening 341 formed on the lid 34. Since the lid 34 has the opening 341, gas or liquid outside of the lid 34 may enter the lid 34. Further, the cavity chamber 35 also has a constant pressure. Therefore, when an external pressure presses the sensor film 32, a pressure difference may exist in the cavity chamber 35, which may be measured by the micro electromechanical element 31. The bonding wires 33 transmits signals to the substrate 30, and the substrate 30 is disposed on an applicable electronic element. A pressure sensing loop is thus formed. However, since a package in which the micro electromechanical element 31 are disposed on the substrate 30 has too great a size, and the electronic element cannot have a reduced volume.
Consequently, a wafer level micro electromechanical package structure process is brought to the art, which uses an etching process to operate a through-silicon via (TSV) process, and performs wafer bonding, so as to reduce the volume of a sensing element. As shown in FIG. 3, which illustrates a wafer level package having a pressure sensor disclosed in US Patent Application Publication No. 2006/0185429, the wafer level package comprises a silicon wafer 40, a sensor wafer 41 having a sensor film 411 that is stacked on the silicon wafer 40, and a glass wafer 42 that is disposed on the sensor wafer 41 by an anodic bonding process. The glass wafer 42 is formed with an opening 421 corresponding in position to the sensor film 411 together. The silicon wafer 40 and the sensor film 411 form a cavity chamber 45. The wafer level package has a sensing principle similar to that of the previously described package, such as further description thereto is hereby omitted. A silicon wafer drilling process is needed to form cavities and blind holes of cavity chamber 45 on the silicon wafer 40. The process is costly and demands sophisticated precision. Therefore, although a pressure sensing element may be fabricated by a wafer process, and a package having a small enough size may be thus obtained, the package is costly because the techniques for fabricating the same are complicated.
Therefore, how to provide a wafer level package structure fabricated by simple enough fabrication steps is becoming one of the popular issued in the art.